Air-operated controller having manually adjustable restrictions giving integral or reset, differential or rate, and proportional band-adjustment modes of operation



Dec. 18, 1956 E. c. GROGAN 2,774,367

AIR-OPERATED CONTROLLER HAVING MANUALLY ADJUSTABLE RESTRICTIONS GIVINGINTEGRAL OR RESET, DIFFERENTIAL OR RATE, ANDPROPORTIONAL-BAND-ADJUSTMENT MODES OF OPERATION Filed April 27, 1953 6Sheets-Sheet 1 a INI'ENTOR.

EDWARD (J. GROGAN ATTORNEY.

DEC. 18, E. C. GROGAN AIR-OPERATED CONTROLLER HAVING MANUAL-LYADJUSTABLE RESTRICTIQNS GIVING INTEGRAL 0R RESET, DIFFERENTIAL OR RATE,AND

PROPORTIONAL-BAND-ADJUSTMENT MODES OF OPERATION Filed April 27, 1953 6Sheets-Sheet 2 Add dPn

d Pn Cn Add INVENTOR. EDWAR D C. GROGAN ATTORN EY.

Dec. 18, 1956 a c. GROGAN 2,774,367

AIR-OPERATED CONTROLLER HAVING MANUALLY ADJUSTABLE RESTRICTIONS GIVINGINTEGRAL OR'RESET, DIFFERENTIAL OR RATE, AND PROPORTIONALBAND-ADJUSTMENTMODES OF OPERATION Filed April 27, 1953 6 Sheets-Sheet 3 INVENTOR.EDWARD C. GROGAN ATTORN EY.

Dec. 18, 1956 Filed April 27 1953 FIG.4

E. C. GROGAN AIR-OPERATED CONTROLLER HAVING M GIVING INTEGRAL OR RESEPROPORTIONAL-BAND-ADJ ANUALLY ADJUSTABLE RESTRICTIONS T, DIFFERENTIAL ORRATE, AND USTMENT MODES OF OPERATION 6 Sheets-Sheet 4 RI l+ RI '2 RH-RZI+TD INVENTOR.

EDWARD c. GR'OGAN BY 2 ATTORNEY.

Dec. 18, 1956 E. c. GROGAN 2,714,367

AIR-OPERATED CONTROLLER HAVING MANUALLY ADJUSTABLE RESTRICTIONS GIVINGINTEGRAL OR RESET, DIFFERENTIAL OR RATE, ANDPROPORTIONAL-BAND-ADJUSTMENT MODES OF OPERATION Filed April 27, 1953 6Sheets-Sheei 5 Zdt R|Cl/ p g Po- PnZ dt R2 RI Cl Ppl PILOT RELAY FIG.5

m2 VALVE F l G. 6

IN VEN TOR. EDWARD C. GROGAN ATTORNEY.

1956 E. c. GROGAN 2,774,367

AIR-OPERATED CONTROLLER HAVING MANUALLY ADJUSTABLE RESTRICTIONS GIVINGINTEGRAL OR RESET, DIFFERENTIAL OR RATE, AND

PROPORTIONAL-BAND-ADJUSTMENT MODES OF OPERATION Filed April27, 1953 6Sheets-Sheet 6 FIG. 7

INVENTOR. EDWARD C. GROGAN ATTORNEY.

United States Patent AIR-OPERATED CONTROLLER HAVING MAN- UALLYADJUSTABLE RESTRICTIONS GIV- ING INTEGRAL OR RESET, DIFFERENTIAL ORRATE, AND PROPORTIONAL BAND-AD- JUSTMENT MODES OF OPERATION Edward C.Grogan, Philadelphia, Pa., assignor to Minneapolis-Honeywell RegulatorCompany, Minneapolis, Minn., a corporation of Delaware ApplicationAugust 7, 1952, Serial No. 303,070

23 Claims. (Cl. 137-86) The general object of the present invention isto provide a novel, elastic-fluid-pressure-actuated, controller,ordinarily an air controller, which is of the force balance type. Theinvention is adapted to provide proportional plus reset control, andwhen desired, to provide rate response also, and is characterized inparticular, by its wide proportional band adjustment range. possibleproportional band range obtainable by the use of the invention mayextend from minus 100% to infinity.

In my copending application, Serial No. 221,501, filed September 17,1951; Patent 2,712,321; issued July 5,

. 1955; I have disclosed and claimed an air controller adapted toprovide proportional plus reset control which comprises separateset-point, measured variable, positive feedback and negative feedbackpressure chambers, cooperating to form a deviation unit. That unitoperates to provide a control force which is a resultant of thepressures in the above mentioned chambers, and is varied inpredetermined accordance with the extent and direction of deviations ofa pressure which is indicative of the deviation of the value orcondition of the measured variable from the predetermined set-pointpressure, and is adjustable through a throttling range of considerableextent.

A primary object of the present invention is to provide a controllerthat will have an adjustable throttling range of practically unlimitedextent.

A more specific object of the invention is to arrange the pressurechambers forming the controller and connect them to one another and tofluid pressure sources so that one of said portions with itsqassociatedconnections will form a pressure and flow network for diflerentiatingthe error, or signal difference, between the process variable and setpoint pressures, and a second portion and associated connections willform a pressure and flow network for integrating the differentialproduced by the diflerentiau'ng action of the first section;

In the preferred form of the present invention, the pressure chambersincluded in the two deviation units, and the pressure chambers formingan associated booster pilot section for transmitting a control pressureto a diaphragm motor valve or other ultimate control element,

controller including essential features of the present invention;

' shown in Fig. 7;

Theoretically, the

Fig. 2 is a block diagram illustrating the manner in which the elementsof the controller illustrated in Fig. 1 cooperate in developing thepreasures and pressure relations used in obtaining the desired controlaction;

Fig. 3 is a sectional elevation of a stack type air controller embodyinga desirableform of the invention shown diagrammatically in Fig. l; I g VFig. 4 is a schematic diagram of a modification;

Fig. 5 is a block diagram of the modification of Fig. 4;

Fig. 6 is a block diagram showing the mathematical relationships of theparts of the modification shown in Fig. 4;

Fig. 7 is a schematic diagram of another modification;

Fig. 8 is a block diagram of a portion of the controller Fig. 9 is aschematic diagram of a portion of a controller according to themodification of Fig. 7 omitting the switch;

Fig. 10 is a block diagram showing the mathematical relationships of theparts of the modification shown in Fig. 7.

In Fig. 1, A designates a first deviation section or unit which, asdiagrammatically shown, comprises a hollow cylinder divided into fourparallel pressure chambers by transverse flexible walls 1, 2, 3, 4, and5. While it is immaterial whether the axes of the unit A and otherelements of Fig. 1 and of Fig. 3 are vertical, horizontal, or inclined,for convenience of description those elements 7 V will ordinarily bereferred to herein as though they were arranged with their axesvertical, as shown. In practice,

are combined in a single stack type air controller unit.

In the preferred form of the invention, the difierentiating andintegrating networks included in a controller, have circuit parametersadjustable to adapt the controller for use under widely differentconditions.

The various features of novelty which characterize my each of theflexible walls 1, 2, 3, 4, and 5, and analogous flexible walls shown inFig. l and Fig. 3, is a flexible diaphragm having a stationary,peripheral portion attached to the corresponding cylinder wall andhaving a movable, central portion connected by an intermediate, flexibleportion to the cylinder. As shown in Fig. l, the transverse walls 1, 2,3, and 4 form the top walls of pressure chambers respectively designatedP0, Ps, Pv, and Fri, and the walls 2, 3, 4, and 5 form the bottom walls,respectively, of the chambers P0, Ps, Pv, andPn. The movable centralportions of the walls 1, 2, 3, 4, and 5 of the deviation section A areconnected by a' transverse rod or shaft B.

A control fluid pressure, which varies in magnitude with changes in acontrol process condition or variable, is transmitted to the pressurechamber Pv by the conduit Pv. A predetermined, ordinarily adjustable,set-point air pressure is transmitted to the chamber Ps by a conduitPs'. For convenience the symbols P0, Ps, Pv and Pn not only designatethe different pressure chambers of the deviation unit A, as abovedescribed, but also designate the fluid pressures in those chambers inpounds per square inch or other suitable unit.

A second deviation section aof the controller shown in Fig. 1, isstructurally like the unit A in that it comprises a rigid, hollowcylinder and transverse, flexible walls or vdiaphragms 1a, 2a, 3a, 4a,and 5a, which are like the walls 1, 2, 3, 4, and .5, in that eachcomprises a central portion connected by a flexible, annular,intermediate portion of the diaphragm to the corresponding stationary,peripheral portion of the latter. The four chambers of the deviationsection a are designated P0, Pn, Pi, and Pita, and those symbolsdesignate the fluid pressures in the corresponding chambers in the samepressure units as thoseused in the deviation section A. The centralporspectively, connected and each serves as an tuator, as is hereinafterexplained;

tions of the walls 1a, 2a, 3a, 4a, and 5a are connected by a transverserod or shaft b. The rods or shafts B and b are coaxial with the flexiblewalls to which they are, re-

air valve ac- The chambers P and Pn of the unit A are connected by apressure equalizing conduit 6 including a regulable reset adjustmentsection or restriction R1. The latter may well be, and ordinarily 'is-a;needle valven The Inpractice, the areas of the flexible walls at the tops and the bottom of each of the pressure chambersPo, Pv,

' chambers Pm and P0 of the unit-a are conne'ctedby a- 5'portional-band-adjustment section 'RZ.

air through the bleed orifice of the nozzle d is controlled pressureequalizing conduit 7 including a re gulable, pro- The latter may be, andordinarily is, 'a-needlevalve. The two chambers Po of the units'Aandaare connected by an unrestricted conduit 8, and the two chambers'Pn ofthe units A are connected by an unrestricted conduit 9 and a J10 Clean,actuating air: under a predetermined, constant pressure, which may 'wellbe 'ofthe order of to '20 pounds 'per square inch, is supplied by a pipeC to the 7 control apparatus shown in Fig. 1'. 'The pipe C is con 15nected'to ableed nozzle D by aconduit ltlincluding a restriction R4, andis connected to'a bleed nozzle d by a I conduit 11 including arestriction R5. The escape of air through the bleed orifice of the bleednozzle D is regulated by a valve E. The latter is shown as of theflappervalve type, and is biased for movement into the position in which itcloses the bleed outlet of the nozzle D. -Normallylthe valve E isdisplaced more or lessfrom the nozzle D by thevalve actuating rod B. eThe outflow of by a valve e like the previously'men'tioned valve E. The

valve e is biased for movement into a position in which it closes thebleed orifice of the nozzle a, but is normally displaced more or lessfrom the latter by the rod or shaft portion b of the deviation unit a.Air under the pressure in the bleed nozzle D istransmitted from'ltheconduit 10 i 'to the chamber Pi of the cleviationseetiona through aconduit 12. The latter isalsoconnected to the conduit 9 through a raterestriction R3. The latter may be a fired restriction, ora needle valveor the like, as conditions; 35

makedesirable; The pressure in the portion of the" conduit 11 betweenthe restriction 'RS'and the bleed nozzle a is ,transmitted by a'conduit13 to the negative. feedback chamber Pna of the devation section a; e

The pressure in the chambers P0 is transmitted through the-conduits 3and 14 to theinlet chamber P0 of a booster pilot section The latter, inthe form shown,

comprises a hollow cylinder and three transverse flexible walls 1b, 2b,and 3b, which may be similar in type to the Walls '1, 2, and 3'of thedeviation section A. As diagram matically'shown, the walls lbrand 2b'fo'rm the top and bottom walls, respectively, of the chamber P0"; andthe walls 2b 'and'3b form thetop and bottomwalls, 'resp'ectively, of. achamber Po' The central portions 'of ,the

, walls 111, 2b, "aha fiblare connected by a 'shaft or rod [211 f. thecontrol pressure chamber g ofthe pilot 'valve G. The

latter ma y well'be of the high capacity, non-bleedytype disclosedintheMoore Patent 2,303,891IofDecembei *1,

{1942, including in" addition to its 1 control 'chamber gk a I 5 fbranch' C, and 'hasits outlet connected through a conduit ,7 V

4 17 to the chamber Po"; and to a diphragm'valve'or otherthenltimate.controlelement I-hf which cooperateswitha flapper valve Ea,a bleedln'oz zle Da and a pilot valve Gto maintairra'controlled'airp'res 'a sure in thecharrlber.Po' j That ratio may well beQandEis 7herein assumed tube, 1 toll ThepressureslomndB6" i are each equal to thepressures in the chambers Potof'the sectionsAandgz.

The nozzle: Dc z recei veslair through a restrictio n from a branch ofthe supply pipe'iC. 'Thefpressurein the bleed nozzlejDZr is transmittedthrough a conduit 15 to controlledairpressure chamber ga. f Thelatterhas? its a inlet connected. through a'conduit 16'to a supply pipe gultimate'control, element H. Thus, on; an increase or a increase ordecreasethepressure'in the chamber g of the pilot valve 6.. Thelatterthen operates in a'known manner to correspondingly-increase or decrease'the p'ressure f in theuconduit, 17;:and thereby in the chamber 110; andin 'decrease in the pressure'transmitted to the chambers Po; and'Po",the boosterpilot section F'operates throughithe' flapper valve Ea andbleed nozzle Da to correspondingly Ps, Pn, Pi, and Pna' are sorelatively proportioned that the pressure in each of said chamberssubjects the correspondingrod or shaft B or b to abias force,jacting onthe 7 rod and tending1to move the latter in the directionindicatedbyjthe smallarrow adjacentgthe rod irileach 'iof the pressurechambers. The bias force to whi chthe rod is subjected by thepressure'in each pressure; chamber, is V proportional to the productot'the pressure'per square inch. in the chamber, multipliedby thedifierential of the areas in square inches of the flexible'diaphragrnsat the i top and the 'bottomfof the chamben lnthedeviation 7 unit A,each, pressure chamber considered by itself, tends to movethecorerspondingirodiB up or down and thereby" 'respectiveiy'decreaseor'increase the pressure in the bleed jnozzle'D, accordingly as thearrow in the pressure chamber points upward or downward. Similarly,thepressure in each of the pressure chambers P0, Pn', Pz', and Pna ofthe deviation unit [1, tends fto'decreaseor increase-the pressure in thebleed nozzle d, accordingly as' thefarrow in the pressure chamber pointsupward or downward. r I

In ordinary practice. the control apparatus shown diagrammatically inFig. 1,-is automatically 'actuatedj on and in response to a variation inthe pressure Pvof the'measured variable, to increase or decrease th'econtrolpressure? transmitted to the ultimate control element l i in thedirec ,tion and to the extent required to 'resto're the predetera minedratio between" me set-point -pressure; Pr and the measured variablepressure Ev The only direct andim a mediate effects on thecontrolapparatus shownin Fig. 1, ofdeviations otthe pressurePv relativeto theipressure' Ps, aside from the pressure variations in the chamberPv,-

are variations'in the pressures in the bleed-nozzles D and V d, andhence in the pressures maintained in and transmitted from the conduit10, 12 directly to the'chamber V 7 Pi and through the restriction R3 toeachof the chambers P 1, and the changeinthe'pressure in the conduit ll,13' transmitted to thepres sure chamber Putt. 2 T

As tpr'eviouslystated, the first deviation section A of Fig. 'l -vvithits associated connections, forms a pressure 5 7 and flow .networkfordifferentiating the error, orsignal diflerenceijbetween the pressures in"the chambersfPsh.

and Pv, while the second deviation sectionf rand asso' 1 '{ciatedconnections form a network-for integrating the diflieren'tial produced;by the'difierentiating action of section A. lnithe operation 'of 'theapparatus shown in Fig;

is an integrating act-ion. I

Apcontroller of thefcharacter shown in Pigs-1; should T flbe suitablefor any. applicationfthatrequires the use of,

the proportional-resetmodofcontrols Itis'to'be'noted i also that asimple re-arrangementaof the componentslinj the control -'circuitqwillpermitprdportional plus; rate; plus! reset response; in fico'ntrolrairfpressuresg-fwto*changes'in deviationbetween the process variable'anjdset point pres sures; or, in responsefto changes in; an the threeterms.i

As previously eitpla irieil, the: symb'ol's llp, ,Pl

the corresponding chambers' of the sectionsA and a' of,Figgil' Otherquantities or coin ponent values hereinafter-takeninto account 'indevelop- 1 ing and explaining l-tlieoperation; of the apparatus shownirhl igxl, arerepr'esented by the symbols i1,,:i 2,'i3, pp, Cn, r1, r2},f3fahd Zo The fsym bolsil, i2, and i3,,rep

resentthe'instantaneous rflow rates through the:conduits a ,br pipe's6,12,};and?7,sirespectivelyl 'Cp represents the 5 *PiaandPhjaQrepresent' thejp ress uresi peri square"'nch in Q;

lumpedor total capacitance of the positive feedback chambers P of thedeviation sections A and a. Cu

represents the total capacity of the two negative feedback chambers Pn.The symbols r1, r2, and r3, represent .the respective magnitudes of theresistances to flow of fluid through the difieren-t restrictions R1, R2and R3. The symbol Z represents the error or difierence between thevariable process pressure 'Pv, and the set point pressure Ps sensedbetween the first deviation section A.

The relative values of the pressures in the different pressure chambers,and of the flow rates to be taken into account in explanation of theoperation of the apparatus shown in Fig. 1, may be developed anddetermined by the use of the following theoretical rules or laws, 1, 2,and 3:

l. Ohms law for electrical circuits may be applied to air flow through aneedle valve or other capillary restriction by the use of the followingequation,

where i represents the rate at which air passes through a needle valveor other capillary restriction, and pd represents the pressure drop ordifference across the capillary restriction, and r represents themagnitude of the resistance to air flow through the capillaryrestriction.

2. At any given instant of time the pressures transmitted to thenegative feedback chambers through flappernozzle action, will maintain abalance of forces within the respective deviation sections A and a.

3. The nozzle pressure required to achieve force balance within therespective deviation sections do not exceed the supply pressure. 7

The foregoing rule or law 1 is accurate when the pressure drop acrosseach capillary restriction is small in comparison with the average levelof the absolute pressure. The foregoing rule or law 2 will hold truewhen the air bleed rate through the nozzle D of the first deviationsection of Fig. 1 islarge compared .to the parallel bleed rate throughthe restriction R3; and the bleed rate through the nozzle d of thesecond deviation section is large compared to the parallel bleed ratethrough the restriction R2. The foregoing rule or law 3 is accurate whenthe nozzle pressures are not requiredto.

exceed the supply pressure to achieve force balance within theirrespective deviation ections.

In using the foregoing assumptions to determine the theoreticalrelationships between flows and pressures within the flow supportshown-in Fig. 1, the arrangement and relative sizes of the flexibleportions of the different diaphragms 1-5 and '1a5a are made such as tomeet the requirements specified in the immediately following paragraphsa and b.

a. The maintenance of force balance in the first deviation section atevery given instant of time requires the relations specified in thefollowing Equations 2, 3, and 4:

dt '7 dt where Z represents the deviation or departure of the variablepressure F1 from the point pressure Ps.

b. The maintenance of forced balance in the second deviation section inevery instant of time requires the relations specified in the followingEquations 5 and 6:

The application of Ohms law to the air currents i1, i2, and i3,respectively flowing through the restrictions R1,

R2, and R3, which have resistances r1, r2, and r3, respectively, is setforth in the following Equations 7, 8, 9, and 10: i

Pt'Pn 7) i3r3=Pi-Pn (8) Pna-Po Pn.-P0

The rate at which pressure builds up in a chamber of a given volume is adirect function of the net -flow or air into the chamber and an inversefunction of the chambers capacitance, and thus explains the followingEquations 11, 12, 13, and 14:

dPn (13-411) dt C12. (11) i3=Cn '+i1 12 dP0 z'l-|'i2 fir Op (13) Hence(i1+i2) Paya 14 Cn and Cp may be assumed to be constants when thechanges in the pressures Pn and P0 are small compared to the respectiveaverage absolute values of said pressures. The above relations may becombined to form the following Equations 15,16, 17, 18, 19, and 20:

' Pn'P0' Z I "7? 71 (15) dPn d(Po+z) z t3-C'n zl-Cn (16) PnaPo Pi'Pn"i3r3 1;? d P0+.-; T32 z r2 r2 r2 r2 n dt 1112 (t1+t2) Q d(Po+z) i C'pC'p T1 12 'dt 73c 12-1-1'3 CW3 CIL73 rlr2 0 1-1 1-2 Ti ,C'pr2 C'pr2 Forarrand G n- C 13 1 m+1 zdt m-1 ]f 7p (19) and the pressure Po may thenbe transmitted to a control valveH through the booster pilot valve G.

The foregoing Equation 18 is a general equation for the control airpressure developed by a controller of the type schematically disclosedin Fig. 1, and operating to provide'the proportional-reset mode ofcontrol. The manner in which the relations developed by the dif- Icontrolair pressure developed, shows that the propor- V portional bandneedle valve R2. Proper :adjustment of ing description and explanations.

of antincr ease or decrease in the pressure Pv is-a move- -pre's'sure inthe nozzle 0. and thereby increases or -de-t cr'eases the pressure inthe chamber Pna;

' Gin the feedback circuit, gavoids unsatisfactory performanceexperienced when a 'high'capacity,non bleed pilot valvetof the typeillustrated and described, operates 40 considerable degree in theresponse in output pressure tem'in. series in the pilot. 1 at theoutputiof the pilot, i. e., the pressure'transmitted to variations inpressuretdeveloped in the positive betweenfthe two positive'feedbacklcharnbers P of the deviation sections A 'anda insureslthat thetpressurelevel in-.the first g deviation'section willjnot' becomeequalto j furthera desirable 'efiect of free communication between f thetwo positive'feedback'chambers is the proyision of;

additional gain stage through regeneratiyef'teedback t action. It isfurther to 'be noted, that "in a case in" which the error'signal':developed' across thfifI'ESitZlIlCC R3 bethe rc ontrol air pressurewill continue to varythr'ough -1sponse to changes in amaze tionalband'PB fof the unit (Q+,coeflicient ofithe'vZ termlmaybe expressed bythe following equationzi Thus, the proportional response of the unitwill not'be influenced by the setting of the reset needle valve R1;

and the proportional band BB maybe varied' from so (when r2 to-O (whentr2=r3). However, it can be seen that the coefiicient of thezdt term (aswell as 10" the z; term) will be influenced by the setting of the prothereset needle valve Rlf'however, should permit any "desired resetresponse at any given setting of the needle valve R2. It is'interesting'tomote that with propor- 15 i tional response cut-rofiti.e., when fl s the equation for control ?air pressure reduces to a mentof the rod B'Which increases or decreases the bleed pressure in thenozzle D, and thereby increases orde creases the pressures in a the twonegative feedback chambers Pn and in the chamber P1. The changes: in

the pressure Pi and in the negative feedback chamber P1: of thedeviation section a, results in a movement of' V the rectorshaft'liwhich increases or'dec'reases the bleed '3' i) Thejbooster'pilot" section F with the non-bleed pilot alone: (is e., open looped) asan isolation or gain relay. 'Insuchi cases, hysteresis and/drift areevident to a to changes in the pressure applied-to theinput chamber ofthe pilot valve. However, the arrangement illus trated in theboosterpilot valve section Fof Fig. 3 is designed to correct this condition inthat it permits the inclusion: of :a high gain flapper-nozzle detectionsyst Thus the pressure developed 5 to the control element H, is'made-"extremely sensitive t feed back chambers of devi'ation sections Aand a; r a

It is to be noted that the sizing of the passage through i therestriction element R3, or. more accurately," the magf nitude of'theresistance to airflow through the restriction R3, maylbe varied as'theconditionsof controller application make. -tdesirfable The treecommunication the'supply pressure before the outputpressure from theseicrond deviation gaireaches its full scale value Thej latter may be assumedito bef iabout 15 ts. 'A

comes too weak to be sensediby the deyiation sectional,

reset action in/the first deviation section until the prioc: a

t esskva riable fioats infto'the control point;

Proportional'plus reset and plus rate' c ontrol in is} the quantity Z,may betincluded, t.

-' control valve.

- restrictions ,Rl, R2,'R3,*R4,- R5, and-R6 are associated that in whichthe conduits 6,7 ,and' 9 17, are a's soc iated' 9:

'with the corresponding chambers of Fig. 3.

chambers 'Airn -in treecommunication with the atmos 1 V ;phere.. Theflexible walls o f thesecondjdeviation sec.. tion a, are connected byatcentral sha ft'or rjo'd bT which i pressures in'. the correspondingpressure chambers, be-Q V in the pressure developed inthe seconddeviation sec-f t nne f a (22) for three-term controlfthe:pressure;Pnzzmay be transmitted through a'booster pilot to an ultimate i Ifthe'resistance R3,is a needle valve;

restriction, the coefiicientot the v V I 27f terms may be adjustedtotheir dcsired valuesgf g a c In Fig. 3 I have illustrated,somewhatfldia'g'rammatically, a stack type instrument structure 'Qadapted for operation in the manner illustrated-in Fig. land in Fig. 72. U The stack' structure comprises rigid, hollow, eircu- 7 lar bodiesarranged end'to end, and flexible wall or di-f 'aphragm t mernb'ershaving. their peripheral portions clampedbetween the ends-of adjacentrigid stacli elel'- merits," The arrangement shown in'Fig. '3' di1'fersfrorn that shown in Fig. "l in that each ofthe flexibletwlalls for'mingone side wall/of apressure chamber, is interposed between that chamberand a chamber Atm, which is open tome atmosphere In the particulararrangement shown ,in Fig. 3,'the' pressure chambers Pn, Pv, Ps,*andj-Pb, extending in the *order stated downward from the-top of thestructure Q, constitute the four pres 1 I sure chambers ot' thefirst'devia tion section A. The i chamber Po at the bottom of thesection A also forms 5 theztop portion-of the tdeviation sectionr 'Iheremain ing pressure chambers 'Pn; Pi, and Pna' of the seetion a' arerelatively arranged as shown in 51; The four,

/ llower charnbersof the stack'unit are"eollective1y,anal togoiis-tojthe booster-pilot section andpilot valve chant Conduits Ps'anew "are connecteid to ;the pressure chambers Ps and Pv, respectively,ofiFig; ,3; Conduits t 11'; 12' 15", 14', 15', 16', a nd 17', and' awiththe chambers Pp, P'n, Pi, Pna, P0-',*P0", g, andgqt t of Fig.3, inamanner generally similar or'analogous'to Restrictions? t Rl-R6are'jrespectivelyfassociated with the chambers 'PQ,' Pi,12I1Z,"PO';VPO'Z' g and ga of Fig.1. The'fleiiible V chamber walls(sf/the deviation section A are'c'onnectegl' by afeentral shaft or redBflfwhieh cooper ates'witha" flapper valve E. to control the foutflow ofair through the .bIeeden'noznle'DT ZT he latter differs frorngthenozzleDf or at only in that it is located=within ouetof the staclcmove'siin response .to variationsiin the resultant of thev tween .alower position in'which it icloses gand an upper,

position in' which it opens a -vent or'bleederroutlet d from thenegative feedback 'chamber lfna'xat the bottom" oftliedeviationfsection.

A'cen tral rod or shaft bbi connected toithe three upper;

tmost fiexibleiwall gelements of' the. booster-pilot'valve a sectionFGoffFig it" controls ta .vent Dri openingfrom the subjacent pressurechamber g""td an adjacent atg f mospheric pressure chamber Aim. The twolower flex-f ible wall members of the'valve section P6 of the stackassembly, are con nect'edttoa tubnlar valve ntemberlllgi The latter is'formed with; a central passage 21 which is c'losed a't its-upper end andis open at its lowerlend, and j is also formed with lateral vents;22opening;totheati mospheric pressure chamber Aim betwee'n'fthechambers g and g". The lower end of the valve member 20 extendslooselythrough an opening 23 in the top wall of a valve chamber 24. As shown,the chamber 24 is formed in the bottom end wall section of the stackassembly unit Q and is connected by conduit sections 16' and 11 to themain air supply source C. A ball valve 25 within but not filling thechamber 24, is spring biased for movement into engagement with the lowerend of the top wall opening 23 of the chamber 24, so as to therebyprevent the passage of air out of the chamber 24 to the atmospherethrough the passage 23. As shown, thearea of the flexible bottom wall ofthe chamber g is substantially greater than the area of the flexible topwall of the chamber ga'. The chambers ga and P" are in freecommunication through a conduit 26.

The booster-pilot section is in effect an additional relay section witha non-bleed pilot in the feedback circuit. High capacity non-bleedpilots of the type illustrated in Fig. 1 do not give satisfactoryperformance when operating alone (i. e., open looped) as isolation orgain relays. Hysteresis and drift are evident to a considerable degreein the response in output pressure to changes in the pressure applied tothe input chamber of the pilot. However, the arrangement illustrated inthe booster-pilot section of Fig. 3 is designed to correct thiscondition in that it permits the inclusion of a high gain,flapper-nozzle detection system in series in the pilot. Thus thepressure developed at the output 17' of the pilot (i. e., the pressuretransmitted to a control element) is made extremely sensitive tovariations in pressure developed in the positive feedback chamber Powhich is common to the deviation sections A and a of Fig. 3.

In the operation of the controller comprising the two deviation units Aand a, the effect of the second deviation unit a is to create an outputpressure P0 which is proportional in magnitude to the variable pressurePv under measurement. Pressure Pv forms the input to chamber Pv of thefirst deviation unit. The output pressure P0 of the second deviationunit is applied by the connection 8 to the positive feedback chamber P0of the first deviation section A for the purpose of regulating theeffective follow-up action on the rod B of a change in pressure in thenegative feedback chamber Pn. A particularly important feature of thearrangement is the'provision of the adjustable restriction R2 whichconnects the negative (Pna) and positive feedback chambers (P0) of thesecond deviation section a and permits adjustment in the magnitude ofthe said output pressure of the second deviation unit and therebypermits variation in the extent of followup action produced by a changein pressure in the negative feedback pressure chamber Pn of the firstdeviation section. Thus, adjustment of the restriction R2 provides aproportional band or throttling range adjustment of the controllercollectively formed by the deviation sections A and a.

Let it be assumed that the adjustable reset restriction R1 is closed.This restriction is in the connection 6 I between the negative feedbackchamber Pn and the positive feedback chamber P0 of the deviation unit A.Proceeding on this assumption, on a change in the measured variablepressure applied to the chamber Pv, the deviation section A operatesinitially to produce a pressure in the nozzle D which is comprised of acomponent proportional to the magnitude of the variable measuredpressure and a component proportional to the rate of change of themeasured variable pressure. That pressure is applied directly byconnection 12 to the pressure chamber designated Pi of the deviationsection a. The pressure in the negative feedback chamber Pn of deviationsection A, proportional to the measured variable pressure, is applied bythe connection 9 to the chamber Pn' of deviation section a. It will benoted that the pressures in chambers Pi and Pa apply opposing forcestothe rod b, and

v as those skilled in the art will'readily understand, the

sentative only of the rate of change of the measured variable pressure.In other words, thereexists in each of the chambers Pi and Pn a pressureproportional to the measured variable pressure and since those pressuresare opposed, they effectively cancel each other, leaving only the ratecomponent of pressure in the chamber Pi efiective to act on the rod b.

The motion of the rod b resulting from the application of the ratecomponent of pressure in the chamber Pi is efiective to cause a changein the pressure in the nozzle d of deviation unit a, and that nozzlepressure change is applied by connection 13 to the negative feedbackchamber Pna. The pressure change so produced in chamber Pna provides afollow-up or balancing adjustment tending to restore the rod b to itsinitial position. In other words, the change in pressure in chamber Pnais in the direction opposing the rate component of pressure in thechamber Pi.

By virtue of the connection 7 including the adjustable restriction R2between the negative feedback chamber Pm: and the positive feedbackchamber Po, the deviation unit a operates effectively to integrate therate component of pressure existing in the chamber Pi. Such integratingaction thus produces in chamber P0 a pressure which is proportional to'the component of pressure in the chamber Pi which is representative ofthe measured variable pressure Pv. 'It can be demonstrated that, byadjustment of the size of the restriction R2, the magnitude of thepressure produced in the chamber Po can be varied at will over a wideoperating range, specifically, from zero to the pressure of the supplysource connected to the conduit C.

As shown, the chamber P0 of the deviation unit a is connected byconnection 8 to the chamber having the same reference character (P0) ofthe deviation section A. With chambers in the deviation section a ofsuitable volume in relation to the size of the restriction R2, there isat most only a small time delay between the application of a change inthe' measured variable pressure in chamber Pv of unit A before thatchange in pressure is felt in the positive feedback chamber Po. Analysisof the arrangement of deviation unit A shows that the effect of applyinga pressure in the chamber Po which is proportional to the measuredvariable pressure is to regulate the eflectivenegative follow-up orbalancing action on the rod B of a change in pressure in the negativefeedback chamber Pn. Moreover, the extent of such regulation isadjustable by manipulation of the restriction R2. Such regulation in theeffective balancing action produced by a change in pressure in. thenegative feedback chamber Pn is known as a proportional band orthrottling range adjustment. Accordingly, adjustment of restriction R2permits-a desirable adjustment of the proportional band or throttlingrange of the controller actuated by elastic fluid pressure as described.Furthermore, the cooperation of the two deviation units A and a is suchthat the proportional band or'throttling range may be adjusted over awide rangefrom zero to infinity.

In the foregoing explanation, it has been assumed that the adjustablereset restriction Rlin the connection 6 between the negative andpositive feedbackchambers of the deviation unit A has been closed. Whenrestriction R1 is closed, the elastic fluid actuatedcontroller'described produces no reset action. When restriction R1 is opened topermit a regulated flow of elastic fluid between the negative andpositive feedback pressure chambers Pn and Po, the operation oftheapparatus is similar to that stated in the foregoing explanation,except that the resultant force acting on the rod B of deviation unit Aincludes a component proportional to the magnitude of the measuredvariable pressure in addition to a component proportional to the rate ofchange of the measured variable pressure. a

As those skilled in the art understand,;the action of the deviation unita in integrating the proportional cone pilot valve regulator G, andaccordingly, control the final Valve orother actuated elementH.

' controlleror directly to a final control. elemenLsuch aS" anair-operated valve. The output of pilot vaIve or relay t p fld t y n 'ifl an ra 'hh a mf l l -l G4? alsopasses jthrough apipe D191 containingarestric 'tion 3R2 which forms the proportional banrtiand resetr'estriction Rl' opena' selected-amount, the pressure in the positivefeedback chamber P0 is made up of a coinponentproportionalto'the'magnitude of the measured variablepressure and the reset"pressure component. Those two components of pressure are applied by theconnections 8 and 14 and by the one-to-one relay F to the Modificationof Figsi4, 5, and 6 'In this modification the error signal istransmitted through an integrating stage ahead of, and in series with, aproportional band plus rate stage. In the; device shown in Fig. 4, rairfrom supply pipe -C passes through restriction 4R5-to'a nozzle d4.Theintegrating stage comprises the chambers and their associatedconnections enclosed within the dotted line designated by the referencecharacter If This integrating stage I :comprises'the separated by twodiaphragms defining between them a a chamber open to atmosphereandmarked ATM. The flexible diaphragms 1d; 2d,i3d, 4d, 5d, and 6d 'areeach connected at its stationary peripheral portion to the correportionconnected by an intermediate 'fiexible portion to the cylinder.Thecentral portion of each of the flexible diaphragms I'd-ed isconnected to a vertically extending 30 spending cylinder wall and eachhas a movable central diagram which shows that the pressure Rviisappliedfin' opposition to Ps. Any difference between these pressures 5 5produces an error signal Z.' This errorsignaltc'ombined with anegativefeedbaek pressure)'iis amplified in the ratio ml by meansofithe'fiapper valve combination d4, V- e4 to produce thez-amplifiedpressure P111. 1 Pressure Pnlwis; split. 7 One portion ofthis'pre'ssnreis fed back 'to 1 '10? epposel the error 'signalZ. The 'otheri portionis fed a through restriction 4R1 to chamber Pp which has a capacity CpL1 Block'lpl shows the mathematical reprc sentation of thetransformationWhichttakes place in the chamber Pp. 'The pressure .Pp is also applied.to the flapper and valve combination D4, E4, whichgives it a 1magnification m2. The'output of the fiapperrnozzle c mbination is fed tothe' pil ottvalve relay ,Gwhere itpr'o-i duces the output pressure Po. 7The 'mathemat'icali representation. of the COIIIPODCHtSZ Of' iIhEoutputjpressure P0 is givenQ Pressure P0 is split." A'portionoftptessure Po f is fed back to, ChamberPnZ whichhasir'esistan'ce 4R2 andcapacity C122. The separatejblock PnZ lshows'jhe mathematical representation ofgthe efiects applied to the'pressureincha'mber N Fig. 6,is a diagrammatioshowingof a mathematicalequation of theway in which the error signal Z is made up of thepressures, resistances, and capacitances referred toinFigsAandS, V a aModification'ofFigsj, '8, 11M210 7 Fig. 7 shows a controller in whichthe pressure pro- H portional to the instantaneous value of theprocessor measuredrvariable is supplied to the controller through a pipePr; A pressure proportional to thatva'lve' of the r rod' or shaft'beiRod or shaft b4 actuates a flapper e4 measured'variable (which it isdesired to have the conwhich is biased into the position in which itcloses the bleed outlet of the nozzle :14; Normally, 'the valve e4 isdisplaced more or less from the nozzle d4 by the valve actuating rod'bi,jThe chamber Pnl is connected under the control of 'Inozzle' d4 by pipesD11 and D13. Charn 'ber Pp is connected to nozzle d4' by pipes D11 andD7containing a manually adjustable restriction: 4R1 which' forms theproportional band adjustment. p 7 i The proportional band plus ratestage, which performs t the differentiation, is formed by the chambersand dia- 'phragms and their associated connections enclosed within tthedot tedline marked iwith the reference charactenD; 7 These are thediaphragm 7d-which forms tthe upperf flexible wall of the chamber Pp,and the diaphragm 8d,; 7 V which form'sthe lewe nexible wall 'of' thechamber P112; s r D; Th automatic r Stage mprises the; 7

which is the negative feedbachycha nber and twhichiha "a capacity C112;.The diaphra ms 7d and 8d arejcon nected by at-valve-actuatingshaftor'r'od B iQwhic'h actu-j, ates a fiapperiE ErrelatiVetOa'nozz'leiD4; Nozzle @134 through which theoutput pressure(Pbyi'sjtedtojaiiothelt adjustment.) Pipe Di is connected at itsopposite end.

to 'fthe-seicondfnegative feedback lchamberPnZl I portien connected'.byan intermediate flexiblepo" troller maintain is fed to the controllerthrough pipe which the measured variable pressur'e Pv and the set point4 pressurePs are applied, can belreversed. "Switching ar-- Vrangement'SW consists ofa valve having a stationary closed within thedotted'lines designated by'the reference a character ARSQ The'controlleralso has a proportiona'l oand-plus'rate stage which comprisesgthe partsenclosed within the'dotted lines designated by the reference char schambers .Pp, 1P1 P5, and F211; j-By operation'of. the V -jswitch SW{the functions ofjth'e chambers P1; and Pscan be i eversed. ',Chambersii pfandlu are separated by two cliaphragms ld'efiriing between themwachamber open to recei ves air-from supply'pipe C through supplylrestrivatmosphere and markedATMl-f Ch m ers Ps andPn 'e hon-4R "Nozzle D4 isconnected to'the motofchamber fg of apil'ot valve or'relay G4 havinganio'utl et pipe D11 the; cylinder. .-;The; central portion; of each ofthe he diaphragrns le-e'is eonnectedjto a vertically extending 1 Fig. iill is'tratesthe rnanneninWhichthe elernentsof i 'iso't pe t t nl h iitoses-t e the confront 7m in Fight combin-ioproduc'e an atpr'essurc'response (Po) that is ja proportional'plus g 7 egral function of theinpnt eiror'signaYlZ) ixe. the v deviationbetween"the-set point pressurePs and the coni V e rolled Tor process variableipressure Pv. This;controller '49. air.pressureiPqfte changes 'in 'n ieasured'orfproee syahj orrns' a' pressurefluid"network'jvhich should permit, a F

theoretical range .in'prep'ortiohal b'and settings from zero toinfinity;:A unique feature'olj thismodifiiifliorristhat magnificatien-cttheQcontroller'jdead spot catising a? 7 V frlrhopigbtweenproceeslvariableand setQpoin't with ex "actuatingrodb'k :7

e:bleedioutleti of"a nozzle. d7. i Normally, the valve e7 "is fdisplacedrnoie "or lessffroin he l'lOZZlfi'd7fb3F l a This controllerpermitsininiediate respoizse'in or H 'nection Ps connected atitsstationaryperipheral portion to the'cer V ible h valve 13 V V V. nectedin series between the process variable connection Pv and the set pointconnection Ps'. At the junction of the restrictions 7R1 and 7R2 isconnected a third restriction 7R3 which comprises a start-up lead timeadjustment. The output of the variable restriction 7R3 leads to oneinlet connection to switch SW.

Air is supplied from pipe C through a nozzle restriction 7R8 to thenozzle d7. Air under the control of this nozzle is fed to the motorchamber g7 of a pilot valve or relay, generally indicated by thereference character G7. The, output of pilot valve or relay G7 is theoutput or control air pressure P and is conducted by a pipe E17 to anair-operated final control valve or to another controller.

A pipe E18 branches from pipe E17 and forms the input to a circuit whichprovides means for adjusting the controller to the characteristics ofthe process under control. This means comprises the parts located withinthe dotted lines designated by the reference character PCA. Thesecomprise adjustable needle valves or other restrictions 7R5 and 7R6separated by a closed chamber whose capacity is designated as 7C4. Theoutput from restriction 7R5 is led to chamber Pn2 which has a capacity7C3.

Fig. 8 is a diagram showing the analog of the process characteristicadjustments to electrical resistances and capacitances.

The proportional band plus rate stage, designated generally by thereference character D, performs the differentiation. This stage isformed by the diaphragm 7d, which forms the upper flexible wall of thechamber Pp, and the diaphragm 7e, which forms a lower, flexible wall ofthe chamber Pnl, which is the negative feedback chamber and which has acapacity 7C3. The diaphragms 7e and 7d are connected by avalve-actuating shaft or rod B7 which actuates a flapper valve E7relative to a nozzle D7. Nozzle D7 receives air from supply pipe Cthrough supply restriction 7R7. Nozzle D7 is connected to chamber Ppthrough manually adjustable restriction 7Riwhich provides an automaticreset time adjustment. NozzleD7 is directly connected to negativefeedback chamber Pnl.

The operation of this modification is as follows. Assume that thepressure in chamber Pv increases due to a variation in the process ormeasured variable. The consequent, upward movement of the diaphragm 2ecauses rod or shaft b7 to lift flapper e7 relative to nozzle :17. Thepressure in nozzle d7 and in the motor chamber g7 of pilot valve orrelay G7 decreases as a result. The pressure in the pipe E17, which isthe output of pilot valve or relay G7, is correspondingly reduced. Sincepipe E18 branches from pipe E17, the pressure in pipe E18, which isapplied to the differentiating means PCA, is also reduced.

The pressure in pipes E17 and E18 contains: (1) a component proportionalto the error signal, i. e. the

difference between Pv, the instantaneous value of the measured variableand Ps, that value of the measured variable which it is desired tomaintain; (2) a component which is a function of the time-integral ofthe error signal. This is also called the reset mode of operation of thecontroller;(3) a component which is a function of the firsttime-differential of the error signal. This is also called the rate modeof operation of the controller. This reduction in pressure in pipe E18causes a flow of fluid from chamber P112 through restriction 7R5,capacity 7C4, and resistance 7R6. The flow through capacity 7C4 andrestriction 7 R6 is proportional to the time-differential or rate modeof operation of the controller. Therefore, the time-differentialcomponent is removed from the pressure in chamber 7C4 so that thepressure in chamber 7C4 contains only the proportional plus the integralcomponents.

/ The flow through restriction 7R5 and capacity of chamber P112 isproportional to the proportional com ponent. Therefore, theproportionalcomponent is removed from the pressure in chamber PnZ so that thepressure in chamber P112 contains only the integral component. Thisconsequent reduction in pressure in chamber Pn2 causes rod or shaft'B7to move flapper E7 away from nozzle D7 and thereby reduces the pressurein the pipe connected to this nozzle. The pressure in the pipe connectedto nozzle D7 contains the proportional plus integral components. Thisreduction in the pressure in the pipe connected to nozzle D7 is appliedimmediately to negative feedback chamber Pnl. A reduction in pressure inchamber Pnl causes negative feedback because diaphragm 6e is moved down,thereby causing rod or shaft b7 to move flapper e7 toward nozzle d7.This is the opposite direction to that in which flapper e7 was moved bythe increase in pressure in chamber Pv.

The decrease in pressure in nozzle D7, simultaneously with itsapplication to negative feedback chamber Pnl, starts a flow throughrestriction 7R4 from positive feedback chamber Pp. This flow throughrestriction 7R4 removes the proportional component and leaves only thetime-integral component in the pressure in chamber Pp.

This reduction in pressure in chamber Pp gives positive feedback to rodor shaft 117 because diaphragm 1e moves up or in the same direction asthat direction in which it was moved by the increase in pressure inchamber Pv. Since the pressure in chamber Pnl contains both theproportional and the integral components, while the pressure in chamberPp contains only the integral component, and since the pressures inchambers Pnl and Pp operate in opposite directions, the integralcomponent is cancelled and only the proportional component is appliedthrough rod or shaft b7 to flapper 27. This proportional componentapplies a force to flapper e7 which is equal but opposite in directionto the force applied to flapper e7 as a result of the error signal.

At the same time, this decrease in pressure in chamber Pp gives negativefeedback to rod or shaft B7 because diaphragm 7d move down therebycausing rod B7 to move flapper E7 towards nozzle D7 or in the directionoppositeto the direction in which flapper E7 was moved by the reductionin pressure in chamber P112.

A decrease in the pressure applied to chamber Pv, as a. consequence of achange in the process or measured variable in the opposite direction tothat just described, will obviously cause each of the movements justdescribed to be reverse but will cause the positive and negativefeedback chambers to operate so as to assist or oppose, respectively,the movements of the flapper-actuating rods caused by the change in theprocess or measured variable.

Fig. 9 shows that the process variable connection Pv' maybe connecteddirectly to the chamber Pv and the output of restriction 7R3 can beconnected directly to the chamber Ps. When this is done, the switch SWis omitted. This drawing illustrates the connections for reverse actionof the controller.

Fig. 10 (Sheet 4) is a block diagram of the pressure divider-delaycircuit comprising the resistances 7R1,

7R2, and 7R3. The transfer functions appearing in Fig.

10 are based on the assumption that the capacity 7C1 of the chamber Pvor Ps is very small in value. Therefore, for any appreciable delay inmodified set point pressure, resistance 7R3 is very much greater than7R1 or 7R2. The pressure divider-delay circuit gives desired start-upcharacteristics and recovery of the measured variable to the controlpoint without overshooting of the control point. In effect, thecomponent of control air pressure (P0) that opposes the effect of thesystem lag for optimum control is derived from the inclusion of theprocess characteristic adjustments (PCA). These provide a pneumaticanalogue of the dominant process characteristics in the feedback of astiff circuit. The automatic reset time adjustment 7R4 governs the rateat which the measured variable is permitted to return out acorresponding use of other features.-

" tforce' Whichfis the'resultant of said forces.

. said forces. 7 v y 7 3. An elastic fluid pressure actuated controller,includ-- ing, means to create a process v ariable'force proportional tothe deviation of a processvariable from a predeterembodiment of myinvention now known to 'rne, it will 5 be apparentto those skilled inthe art that changes may be made in the form of the apparatus disclosedwithout departing from the spiritof my inventionas set forth, fin theappended claims and that in some cases certain Having now described myinvention what I' claim as. new anddesire tosecure by Letters Patent isas follows 5' pressure amplified chamber, means responsive'to the re a 7sultant of the pressures in first four pressure chambers regulating thepressure insaid input chamber, means de- 7 V pending on the resultant ofthepressures in the second deviation section forsupplyingelasticfluidiunder regu-i lable pressure to the'negative feedbackpressure amplified chamber of the'second'deviation section, meansresponfeatures of my inventionmay be used to advantage with- 10 V V V rtive feedback pressure chambers, and means; for varying 1..Anelastic-fluid-pressure-actuated controller, including, ,means to derivea process variable force proporl5 ponent proportional to said processvariable, means responsive to said second force to create a third forcecon- 0 taining a component proportional to said process variable plusthe derivative of said deviation with respect to time, means "to opposesaid second force and said third force to each other to create a fourthforce proportional to said derivative of said deviation with respect 5the first 'negatlve feedback chamber which pressure is totime, means tointegrate said fourth force proportional to the derivative of saiddeviation with respect to time so 1 as to create a fifthforce-proportional to said deviation,

and rneans'to oppose' said process variable force and said fifth forceto said third force'to producean' o'utputBQ 2. An elastic fluid pressureactuated controller, includ-' ing, means to create a process variableforce proportional to the deviation of a process variable from apredeten mined value, means responsive to said' process vanable 3 forcetocreate a'second force prop'ortional' to said devia= 'tionf meansresponsive to said second force to'create a negative feedback forceproportional to said deviation plus the derivative of said deviationwith respectftoitime, 7 means inwhich said negative feedback force andsaid Q second force rea er-me e produce; a third forejejpropor- V tionalto the'derivative to said deviation withrespect to time,'meanscreatingjan elastic fluid pressure flow proportional to thederivative of said deviation'with'respect to itime,rnanually adjustablemeans for integrating-said Q flowl to createa fourth force proportionaltosaid deviation, and meansin' which said process variable force andsaid fourth'force oppose said negative feedback force to create anoutput which is proportional to the resultant of r a e v d sivetovariations in the resultant of the pressures in the pressure chambersofthe first deviation s'ection and of the second deviation section, meansconnecting the posi:

the pressure of elastic fluid froma source of'elastic fluid,

thelast mentioned resultants. Y

5. An elastic fluid pressure actuated controller, including, a firstdeviation section comprising a first positive feedback pressure chamber,a set point pressure chain: her, a process variable pressure chamber,and a first negative feedback pressure chamber, and a second deviationsection comprising a second positive feedback pressure chamber, a secondnegative feedback pressure cham her, an input pressure chamber, and "anegative'feedba ck pressure modified chamber, means for transmitting tothe second deviation section an input signal which is a function of therate of change of the pressure developed in pressure chamber, meansdepending on the resultant of the pressures inthe second deviationsection supplying elastic fluid under regulable pressure to the negativefeed.

back pressure modified chamber, and means connecting 7 the positivefeedback pressure chambers to arneans for varying the pressure ofelastic fluid from a source 9f elastic fluid'under pressure andoperating said last men in the process variable pressure chamber and theset tioned means in accordance with the resultant of the' pressuresinfsaid sections.

6. vAn elastic fiuidpressure actuated controller includ-T- ing, a firstdeviation section tcomprisingia first-positive f Y feedback pressurechamber, a set point pressure; charn-E V berg-a proessvariabl' "pressurechamber, "andt'a first,

negative feedback pressure chamber, and asecond devia tion sectioncomprisinga second positive feedback'pres-j V v sure chamber, a secondnegative feedback pressurexhanrf her, an input pressure chamben'anda'negative feedback pressure modifiedchamber, means responsive to the remined valuc, means responsive to'said process'var'iablei variableforce, means to createa negativefeedbackforce said deviation withrespect to tifnes'oa's to create a fourthifforcefproportional'to saiddeviation, and means to 7 apply said process variable force and saidlfourth forcein oppo-, sition to said negative feedback force to p'roduceanioutput force which is-the resultant'of saidforcesl T t r t i 4. 'Anelastic fluid pressure actuated controller, includfeedback ,pressurechambe'r, aprocess variable pressure chamber, a set point pressurechamber, and a first nega; trvet feedback pressure'chamber, and aseconddevia tion section'comprising a second positive feedback pres surechamber, a second negative feedback pressure cham- =ing, a firstdeviation section comprising a first positive I, 7 J V V 7Q a negativefeedback chamber, and means connect ng the, r

output of the booster pilotsectioni'to, the negativefeedan fl? r r and an g tive feed c 75 sultant of the pressures in the first four chambersregu lating' the pressure in said inputbhamber, means coir- 0 nected tothe pressure in said input chamber ,and to said ffirst andsecondnegative feedback pressure chambers and introducing into the pressure insaid input chamber a pressure component proportionaljtoj h fifi g'diiference between the pressures, in said" process variable;

pressure chamber and'said setpoint pressure chamber V V and said firstpositive feedb'ack pressure eh'amberf-means' I dependingon; theresultant .of the pressures in the second four pressure cliambfers'supplying elastic fluid linderregu-a I lable pressure, to .the'negative'sfeedback' pressure rn'odi-Q fied chamber, lmeans connectingthe'negatiyefeedback pressure modified chamber to vthe secondpositivefeedback 7 pressure I chamber, jn'ieanjs" integratingthe flow offiuid between;said chambers to provide in saidfirstaand j" 1 secondpositive vfeedback "pressure ,lchamber'sjfa pressure" 5componentproportional to the diiferencejbetween the i w 7 pressures insaid second negative feedback pressure'chamher and said input chamber,-means connecting'said'first and said secondpositivefeedbackpressurechambers'to ajbooster pilot section havingranoperating chamber and],

back chamber of saidboosterpilot-section."

u d; irz i sl t s, a fi st d i tio Section comprising first positivefeedback'chamber aset pointchamber, a; e

r 741A controller actuated by the pressureofgan' elastic i processvariable chamber, and a first negative feedback chamber, and a seconddeviation section comprising a second positive feedback chamber, asecond negative feedback chamber, an input chamber, and a negativefeedback pressure modified chamber, a valve responsive to the resultantof the pressures in the first four chambers and regulating a pressure,means connecting the pressure regulated by said valve to said inputchamber, a first restriction connected between the pressure regulated bysaid first valve and said first and said second negative feedbackchambers and having a capacity for fluid flow less than that of saidfirst valve, a second valve responsive to the resultant of the pressuresin said second deviation section and regulating a pressure, a connectionbetween the pressure regulated by said second valve and said negativefeedback pressure modified chamber, a second restriction between saidnegative feedback pressure modified chamber and said second positivefeedback chamber and having a capacity for fluid flow less than that ofsaid second valve, a connection between said first and second positivefeedback pressure chambers, and a connection for the output pressure ofsaid controller from said first and second positive feedback chambers.

8. An elastic fluid pressure actuated controller, including, a firstdeviation section comprising a first positive feedback pressure chamber,a set point pressure chamber, a process variable pressure chamber, and afirst negative'feedback pressure chamber, and a second deviation sectioncomprising a second positive feedback pressure chamber, a secondnegative feedback pressure chamber, an input pressure chamber, and anegative feedback pressure amplified chamber, means responsive to theresultant of the pressures in said first deviation section and varyingthe pressure of the fluid from a source of fluid pressure, meansintroducing into the fluid pressure from said source a pressurecomponent proportional to the derivative with respect to time of thedifference between the pressures in said process variable pressurechamber and said set point pressure chamber and said first positivefeedback pressure chamber, means integrating said pressure containing acomponent proportional to the derivative of said deviation and toproduce a pressure proportional to said deviation, and means applyingsaid last mentioned pressure proportional to said deviation to a motorcontrolling the pressure of a fluid from a source of fluid to furnish anoutput fluid pressure.

9. An elastic fluid pressure actuated controller, including, a firstdeviation section comprising a first positive feedback pressure chamber,a set point pressure chamber, a process variable pressure chamber, and afirst negative feedback pressure chamber, and a second deviation sectioncomprising a second positive feedback pressurechamber, a second negativefeedback pressure chamber, an input pressure chamber, and a negativefeedback pressure modified chamber, means responsive to the resultant ofthe pressures in the first deviation section and varying the pressurefrom a source of fluid pressure to provide a pressure having a componentproportional to the deviation between the pressures in said processvariable pressure chamber and said set point pressure chamber and saidfirst positive feedback pressure chamber, means differentiating apressure containing said component proportional to said deviation toprovide a pressure proportional to the derivative with respect to timeof said deviation, means integrating said pressure proportional to thederivative with respect to time of said deviation to provide a pressureproportional to said deviation, means applying to said second deviationsection said pressure proportional to the derivative with respect totime of said deviation and said pressure proportional to said deviation,means connecting said first positive'feedback pressure chamber to saidsecondpositive feedback pressure chamber to equalize the pressure of thefluid in said chambers, and a third deviation section having a motorchamber connected to the pressure in said positive feedbackspressurechambers so as to be actuated thereby.

10. An elastic-fluid-pressure-actuated controller, including, a firstdeviation section comprising afirst positive feedback pressure chamber,a set point pressure chamber, a process variable pressure chamber, and afirst negative feedback pressure chamber, and a second deviation sectioncomprising a second positive feedback pressure chamber, a secondnegative feedback pressure chamber, an input pressure chamber, and anegative feedback pressure modified chamber, means responsive to theresultant of the pressures in the first deviation section and varyingthe pressure from a source of fluid pressure to provide a pressureproportional to the deviation between the pressures in said processvariable pressure chamber and said set point pressure chamber and saidfirst positive feedback pressure chamber, means differentiating apressure containing said components proportional to said deviation toprovide a pressure proportional to the derivative with respect to timeof the deviation, means integrating said pressure proportional to thederivative with respect to time of said deviation to provide a pressureproportional to said deviation, means responsive to the resultant of thepressures in said second deviation section and regulating the pressurefrom a source of fluid pressure and applying said pressure to saidnegative feedback pressure modified chamber, means connecting said firstnegative feedback pressure chamber and said first positive feedbackpressure chamber together and operable to produce .in said firstpositive feedback pressure chamber a pressure component proportional toreset, a third deviation section having a motor chamber and a negativefeedback chamber, means connecting said first and said second positivefeed back chambers to said motor chamber so that the pressure in saidpositive feedback chambers operates said third deviation section, andmeans connecting a pressure responsive to the output of said thirddeviation section to the negative feedback chamber of said thirddeviation section;

11. An elastic fluid pressure actuated controller, including, a firstdeviation section having four chambers therein, a second deviationsection having four chambers therein, a third deviation section havingtwo oppositely acting pressure chambers therein, means responsive to theresultant of the pressures in the chambers of said first deviationsection regulating the pressure in one of the chambers of said seconddeviation section, means responsive to the resultant of the pressures inthe chambers of said second deviation section regulating the pressure inanother chamber of said second deviation section, means responsive toboth of said resultants regulating the pressure in 7 one of the chambersof said third deviation section, and means responsive to the resultantof the pressures in the chambers of said third deviation section andregulating the pressure in the other of the chambers of said thirddeviation section. V

12. A controller actuated by the pressure of an elastic fluid,including, a first deviation section having a plurality of chamberstherein including a first positive feedback chamber and a negativefeedback chamber, a second deviation section having a plurality ofchambers therein including at least a negative feedback pressuremodified chamber, and a second positive feedback chamber, a first valveresponsive to the resultant of the pressures in the chambers of saidfirst deviation section and regulating a pressure, a first restrictionconnected between the pressure regulated by said first valve and saidnegative feed back chamber and having a capacity for fluid flow lessthan that of said first valve, a second valve responsive to theresultant of the pressures in the chambers of said second deviationsection and regulating a fluid pressure, a connection between thepressure regulated by said second valve and said negative feedbackpressure modified chamber, a second restriction connected between saidnegative feedback pressure modified chamber and said secondpositivefeedback chamber and having a capacity for fluid flow less than that ofsaid second valve, and a third restriction connected between saidnegative feedback chamber and said positive feedback chamber, thepressure in said positive feedback chamber being the output pressure ofsaid controller. V V

13, A controller actuated by the pressure of an elastic fluid,including, a first deviation section having a plurality of chamberstherein including a negative feedback pressure chamber, a seconddeviation section having a plurality of chambers therein including apositive feedback pres- .surechamber and a negative feedback pressuremodified chamber, a first valve responsive to the resultant of thepressures in the chambers of said first deviation section, a firstrestriction connected between the pressure controlled by said valve andsaid negative feedback pressure chamber and having a capacity for fluidflow less than ,that of said valve, a second valve responsive to theresultant of the pressures in the chambers of the said second deviationchambers, a connection conducting fluid at the pressure set by saidsecond valve to said negative feed- .back pressure modified chamber, anda second restriction connected between said negative feedback pressuremodi .fied chamber and said positive feedback pressure chamber andhaving a capacity for fluid flow less than that of said second valve,the pressure in said positive feedback chamber being the output pressureof said controller.

' 14.-A.controller actuated by the pressure of an elastic ifluid,including, a firstvalve operable to derive a pressure containing anerror signal in response to the diflference existingv at, any instantbetween a pressure proportlonalto the process variable and a pressureproportional to that value of the process variable which it is desiredto maintain, a first restriction connected under the control ofsaidfirstvalve, means to operate said first valve in response to thedifierence between a negative feedback pressure under the control ofsaid first valve and a positive feedback pressure which has passedthrough said first restriction to derive a pressure from which theintegral of said error signal has been removed and which is proportionalto said error signal, a second valve, a pilot valve .under the controlof said second valve, a second restriction connected to the outputpressure of said pilot valve,

7 and means for actuating said second valve in response to anydifference between said positive feedback pressure and the pressurewhich has passed through said second restriction to derive a pressurewhich is a proportional plus integral function of the error, signal.

' '15. A controller actuated by an elastic fluid, including,

'a' first valve operable to derive a pressure containing an error signal,in response to the pressure difierence existing at any time between apressure proportional to the process variable and a pressureproportional to that value of said process variable which it is desiredto maintain, a pilot valve connected under the control of said firstvalve and operable to produce an output signal, a first restrictionconnected to the output of said pilot valve, a second valve, a secondrestriction connected to a presbetween the pressure under the control ofsaid second valve and the pressure which has passed through said 7second restriction to derive a pressure having a component-proportionalto the'integral or reset mode of operation, and means actuating saidsecond valve in response to any difference between the pressure whichhas passed through said first restriction and the pressure which haspassed through said second restriction to derive a pressure able whichit is desired to maintain, a first pressure-open ated motor connected toone of said conduits, a second sure under the control of said secondvalve, means for actuating said first valve in response to anydifference pressure-operated motor connected to the other;of saidconduits, a first restriction connected between said motors, a secondrestriction and a third restriction connected in series in one of saidconduits, one side of said first restriction being connected betweensaid second restriction and said third restriction. V

' 17. Apparatus for adjusting the proportionalband of a controlleractuated by the pressure of an elastic fluid, said apparatus including,a first valve operated in response to the difierence existing at anyinstant between the instantaneous value of the process variable and avalue proportional to a desired set point so as to derive apressurecontaining a component comprising an error signal proportionaltto saiddifference, a first restriction connected at one side to said pressurecontaining the error signal or to'a pressure proportional thereto, afirst pressure-operated motor connected to be controlled by the pressureat the opposite side of said first restriction, a second valve connectedso as to be actuated in one direction by said first motor, a secondrestriction connected at one side to the pressure controlled by saidsecond valve, a second posite dir'ection to said process variable, saidfirst and second restriction being manually adjustable to vary theproportional band of said controller.

18. Apparatus for adjusting the proportional band of a controlleractuated by air pressure, said apparatus including: an air-supply linesubject to pressure variations; 7

a first flow-line connected to said air-supply line and including, afirst fixed flow-resistance, a first flow-varying I valve, a firstvariable flow-resistance, and a'first motor; a second flow-lineconnected to said air-supply line and including, a second fixedflow-resistance, a second flowvarying valve, a second variableflow-resistance, a second motor, and a third motor; first meansresponsive to the magnitude of a condition for adjusting said firstflowvarying valve in one direction with a force proportional to saidmagnitude; second means for adjusting said first flow-varying valve inthe opposite direction with a force proportional to the magnitude of thedesired value of the condition; said first and second means cooperatingto adjust said first flow-varying valve to produce in said first flowline at a point between said'first fixed flow-resistance and said firstvariable flow-resistance a pressure varying as a function of themagnitude of and of the rate of change of and of the time-integralofsaid condition; said first motor and said second motor cooperating inresponse to changes of pressure therein to adjust said secondflow-varying valve to produceiin said second flow-line at a pointbetween said second fixed flow-resistance and said second,variable-flow-resistance and in said third motor a pressure varyingsubstantially proportionally tof w a function of the magnitude .ofand'to the time-integral termine the width of thepropo'rtional banddofthe con- 7 troller by varying the extent of operation of said first andsecond flow-varying valves in response to a given change.

' in the unbalanced pressures inlsaidfirstand second flowlines 1 V l9.Acontroller actuatedby an elastic fluid, including,

- a firstv lve p r e o r ve a PI 4 1 error signal in response to a firstforce caused by the difier- 21 ence existing at any time betweentheinstantaneous value of the process variable and that value of theprocess variable which it is desired to maintain, a first restrictionconnected to a pressure under the control of said first valve, a secondvalve, 21 second restriction connected to a pressure under the controlof said second valve, means for actuating said first valve in responseto any difference between the pressure under the control of said secondvalve and the pressure which has passed through said second restrictionso as to move said first valve with a force proportional to the saiderror signal and opposing said first force, and means actuating saidsecond valve in response to any difference between the pressure whichhas passed through said first restriction and the pressure which haspassed through said second restriction to derive a pressure which is aproportional plus the time-integral function of the error signal.

20. Means for adjusting the proportional band or throttling range of anelastic fluid-actuated controller, including, means movable in responseto any difference between the value of the process variable at theinstant and that value of the process variable which it is desired tomaintain, a first conduit connected through a fixed restriction to asupply of fluid under pressure, a first valve in said first conduit andoperable by said means to vary the pressure of the fluid in said firstconduit, a first restriction in said first conduit and connected on itsinlet side to receive fluid at a pressure controlled by said firstvalve, a second conduit connected through a fixed restriction to asupply of fluid under pressure, a second valve in said second conduit, asecond restriction in said second conduit and connected on its inletside to receive fluid at a pressure controlled by said second valve, afirst motor in said first conduit and connected to be controlled by thepressure at the outlet side of said first restriction and engaging saidsecond valve and operating it to vary the pressure of the fluid in saidsecond conduit, a second motor in said second conduit and connected tothe outlet side of said second restriction and engaging said secondvalve and operating it in the reverse direction to the direction inwhich said second valve is operated by said first motor, a third motorin one of said conduits and connected to the outlet side of one of saidfirst or second restrictions and engaging said first valve and operatingit in the reverse direction to the direction in which said first valveis actuated by said means, at least one of said first restriction andsaid second restriction being manually adjustable, thereby to adjust theproportional band or throttling range of the controller, and an outputconnection connected to at least one of said conduits and adapted tosupply an output fluid pressure at a pressure adjusted by the operationsof said first and second valves.

21. Apparatus for adjusting the proportional band of a controlleractuated by the pressure of an elastic fluid, said apparatus including,a first elastic-fluid-conducting network connected at one or more placesto a supply of elastic fluid under pressure, a secondelastic-fluid-conducting network connected at one or more places to asupply of elastic fluid under pressure, first means operable to vary thepressure of the fluid in one of said networks to produce an error signalcomprising a variation in the pressure of the fluid in said networkproportional to the diflerence between the value of the process variableat any instant and that valve of the process variable which it isdesired to maintain, second means operable to vary the pressure of thefluid in one of said networks to produce an error plus rate signalcomprising a variation in the pressure of the fluid in said networkproportional to said error signal plus the first derivative of saiderror signal with respect to time, third means operable to vary thepressure of the fluid in one of said networks to produce a reset signalcomprising a variation in the pressure of the fluid in said networkproportional to the integral of said error signal with respect to time,fourth means operable in response to the interaction of said secondmeans and said third means in opposition to each other to vary thepressure of the fluid in one of said networks to produce an outputsignal comprising a variation in the pressure of the fluid in saidnetwork proportional to said error signal plus the first derivative ofsaid error signal with respect to time minus the integral of said errorsignal with respect to time, i. e. proportional to said error signal,and manually operable means to adjust the speed of operation of saidsecond means relative to said third means and thereby to adjust theproportional band of the controller.

22. A controller actuated by the pressure of an elastic fluid,including, a first valve connected to a supply of elastic fluid underpressure and operable in response to the difference existing at anyinstant between the pressure proportional to the process variable and avalue of said process variable which it is desired to maintain, saidfirst valve being operable to vary the pressure of the fluid to producean error signal comprising a variation in the pressure of the fluidproportional to the difference between the value of the process variableat any instant and that value of the process variable which it isdesired to maintain, a first restriction connected at its inlet side tosaid first valve to receive fluid at a pressure controlled by said firstvalve, said error signal causing fluid to flow through said firstrestriction and to produce a rate signal comprising a variation in thepressure in the fluid on the outlet side of said first restrictionproportional to the first derivative of said error signal with respectto time, a second valve connected to a supply of elastic fluid underpressure and operable to vary the pressure in said fluid, means tooperate said second valve actuated in one direction by the pressure ofthe fluid controlled by said first valve and in the opposite directionby the pressure of the fluid on the outlet side of said firstrestriction, a second restriction connected on its inlet side to thefluid controlled by said second valve, any difference in the pressure ofthe fluid on the inlet side of said second restriction and controlled bysaid second valve causing a flow of fluid through said secondrestriction to produce in the fluid on the output side of said secondrestriction a pressure from which the reset component has been cancelledso that said pressure is proportional to the error signal, second meansto actu ate said second valve and operate it in one direction by thepressure on the inlet side of said second restriction and in theopposite direction by the pressure on the outlet side of said secondrestriction, and third means to operate said first valve by the pressureon the outlet side of said first restriction in a direction to cancelsaid error signal.

23. An elastic-fiuid-pressure-actuated controller, including, firstvalve means operable in response to the deviation of a measured variablefrom a predetermined value to create a first fluid pressure differenceproportional to said deviation, a restriction connected to said firstvalve means and receiving said first fluid pressure difference andacting on a flow of fluid through said restriction to create a secondfluid pressure difference proportional to said deviation plus thederivative of said deviation with respect to time, second valve meansoperable in response to the resultant of said pressure differences tocreate a third fluid pressure difference proportional to the derivativeof said deviation with respect to time, a second restriction connectedto said second valve means and receiving said third fluid pressurediflerence and adapted to integrate the flow of fluid under pressuretherethrough to create an integrated fluid pressure ditierenceproportional to said deviation, and means subjecting said first valvemeans to the force resul-ting from any diflerence between said secondpressure diflerence and said integrated pressure difference.

References Cited in the file of this patent UNITED STATES PATENTS2,360,889 Philbrick Oct. 24, 1944 (Other references on following page)UNITED STATES PATENTS McLeod May 2, 1950 Swenson Aug. 1, 1950 V FitchFeb. 19, 1952 V Eckman Mar. 11, 1952 Griswold et a1 May 19, 1953Ca-ldwell May 19, 1953 Heinz Sept. 8, 1953 FOREIGN PATENTS Great BritainMay 19, 194i I 24 Great Britain 1 Apr.22, 1942 Great Britain ,Apr. 22,1942 Great Britain 1 Apr 13, 1945 France Oct. 5, 1942 1 OTHER REFERENCES

